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Raman Amplification of Matter Waves
With the realization of coherent, laser-like atoms in the form of Bose-Einstein
condensates it has become possible to explore matter-wave amplification, a process in
which the number of atoms in a quantum state is amplified due to bosonic stimulation. In
previous amplifiers based on superradiant Rayleigh scattering the atoms remained in the
same internal state [1, 2], a fact that severely limited the performance since the amplified
atoms were scattered out of the final state or served as a gain medium for higher-order
processes. We have now realized a Raman atom amplifier in which the gain medium and
the amplified atoms are in different internal states [3]. Such a system has analogies to an
optical laser in which different transitions are used for pumping and lasing.
The gain mechanism is provided by a polarization grating, a coherence between two
different hyperfine states. We observed an exponential growth of this grating and
characterized its coherence time.
Observation of superradiant Rayleigh scattering. (A) Experimental configuration. A laser beam (wave
vector k) is incident perpendicularly to the long axis of the condensate; its electric field vector E is parallel
to it and the applied magnetic field B. Each scattering event results in a recoiling atom (momentum =q)
and a scattered photon (momentum =(k-q)). The recoiling atoms lie on a shell of radius =k. (B)
Spontaneous Rayleigh scattering. The absorption image shows a halo of atoms. The intensity of the beam
was 1 mW/cm2; the pulse duration was 1 ms. (C) Superradiant Raman scattering as observed for a beam
intensity of 18 mW/cm2 and a pulse duration of 100 µs (the original condensate was fully depleted after
∼10 µs). In both cases the field of view was 1.05 mm x 1.05 mm.
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amplification of matter waves, Science 286, 2309 (1999).
D. Schneble, G.K. Campbell, E.W. Streed, M. Boyd, D.E. Pritchard, and W. Ketterle, Raman
Amplification of Matter Waves, preprint cond-mat/0311138.